Is the virtual study as good as conventional colonoscopy?
By Robert E. H. Khoo, M.D., F.R.C.S.(C), F.A.C.S.
June 12, 2004Copyright CCCRS 2004

Colorectal cancer is the second biggest cancer killer. It will kill more than 56,000 people this year in the U.S. The good news is that the survival rate is 90% if it is caught early. Traditional screening methods are barium enema x-ray or colonoscopy. Because of negative public perception, many people avoid getting tested. Less than 20% of those for whom screening is recommended actually get tested. Colonoscopy is usually performed by specialists such as gastroenterologists or colon and rectal surgeons. While large metropolitan areas have many of these specialists, small rural counties like Sonoma have a small number of them. In some towns you could wait months for colonoscopy.

A new study published in the December 4, 2003 issue of the New England Journal of Medicine may make screening for colorectal cancer more acceptable. In the study, 1,233 asymptomatic men and women at three hospitals had a virtual colonoscopy and a conventional colonoscopy on the same day. Dr. Perry J. Pickhardt, an associate professor of radiology at the University of Wisconsin Medical School was the lead investigator compared how many potentially cancerous growths, or polyps, each method found.

Virtual colonoscopy detected polyps 10 millimeters or larger in 93.8% of patients while the conventional colonoscopy found them in 87.5% of patients. Conventional colonoscopy was better at finding polyps smaller than 10 mm. The conclusion was that the virtual method was as good if not better than conventional colonoscopy in detecting colon polyps and growths.

When asked, patients preferred the virtual colonoscopy to conventional colonoscopy because of convenience. The virtual study is quicker as well. For both virtual and conventional colonoscopy, a complete bowel prep to clean feces from the colon is required. Both procedures are associated with discomfort, but more patients complained with virtual colonoscopy. No IV sedation is given during the virtual study which may account for this perception. Compared to conventional colonoscopy, the virtual study is free of the risk of bleeding and perforation which is an advantage.

Unfortunately, the technology used in the study is not available in radiology centers around the country that now offer virtual colonoscopies. The virtual studies were performed with advanced scanning equipment and a 3D software rendering tool, made by Viatronix Inc. of Stony Brook, N.Y. Only 50 centers nationwide have this precise 3D technology evaluated in the study.

In order to increase accuracy of polyp detection, patients having virtual colonoscopy were given oral barium to “tag” the stool. Sometimes despite taking the entire bowel preparation, the colon isn’t completely clean. Patients with a poor preparation may have a lot of residual stool which is marked with barium. If an abnormality is seen, a confirmatory conventional colonoscopy is required. This stool tagging may make the follow-up procedure difficult as the endoscopist may not be able to see the colon lining adequately. If a polyp is removed during this follow-up colonoscopy and a perforation occurs, the presence of barium in the colon could result in a life-threatening complication. When barium escapes from the colon it can cause peritonitis which is difficult to manage at surgery. This concern is not addressed in the present study.

Up to 30% of patients have a poor bowel prep at colonoscopy. To some extent, an inadequately clean colon will compound interpretation of virtual colonoscopy, despite using barium to “tag” residual feces.

In this present study sensitivity of conventional colonoscopy for detecting polyps was only 87.5 percent. This rate is significantly below the standard when colonoscopy is performed by experts (>95 percent sensitivity). Remember that this study concentrated on polyps 10 mm or larger. Virtual colonoscopy tends to miss smaller polyps but it is assumed that smaller polyps have less malignant potential. No one knows for sure how big a polyp needs to be before removal is recommended. Some experts believe that most polyps found should be removed or at least biopsied. Small polyps should not be ignored. Would you be comfortable knowing that you were found to harbor a small colon polyp?

Previous studies of virtual colonoscopy have shown that 30% having the procedure need follow-up conventional colonoscopy to check on any lesions that were found.

Douglas K. Rex, M.D., FACG, President of the American College of Gastroenterology and Director of Endoscopy at Indiana University Hospital in Indianapolis says, “Thus virtual colonoscopy is a diagnosis-only test, whereas conventional colonoscopy remains the only strategy that allows both diagnosis and treatment in a single session. The relative cost-effectiveness of virtual colonoscopy, the intervals at which it would be performed, and the risks associated with radiation, remain uncertain."

"One concern I have is that people may assume that virtual colonoscopy is ready for prime time regardless of your approach," Dr. Prickhardt says. He cautions that this is not the recommended screening method for patients at high risk. If you have a positive personal or family history of polyps or colon cancer, symptoms such as rectal bleeding or anemia, you should have conventional colonoscopy.

Virtual colonoscopy is cheaper ($800-$1,000) than conventional colonoscopy ($1,000-$2,500) but Medicare and insurers do not pay for the virtual study. This may change in the future. The virtual study may replace barium enema x-ray. Another issue is coordinating the virtual study with a team of doctors who can do conventional colonoscopy without delay if an abnormality is seen.

To further muddy the waters, on April 14, 2004 Dr. Peter Cotton, a gastroenterologist at the Medical University of South Carolina, published a huge study on the poor accuracy of virtual colonoscopy in the Journal of the American Medical Association. Six hundred and fifteen patients over 50 years of age participated. Virtual colonoscopy missed 61% of polyps under 6 mm in size,and 45% of those under 10 mm in size. Eight cancers were found in these 615 participants but virtual colonoscopy missed 25% of these cancers.

Again the size of the polyp is a major issue. Radiologists seem to prefer a higher threshold value of >/= 1 cm, whereas there are few, if any, gastroenterologists who would feel comfortable ignoring a 6- to 9-mm polyp.

Another concern raised is the radiation exposure with virtual colonoscopy. A recent report suggests that the increasing incidence of abdominal and pelvic cancers may be related to the increased and widespread use of abdominal and pelvic CT scans (remember that virtual colonoscopy is a CT scan).

As I mentioned above, this is an ongoing debate over a developing technology.

As virtual colonoscopy improves and when reimbursement issues are resolved, the study will move into the medical mainstream and lead many more people to get screened for colon cancer.

These images show different views of a colon polyp in a 55-year-old man. Panel A shows the Virtual Colonoscopy overview of the entire colon. Panel B is a computer-generated 3-dimensional “virtual” view of the polyp. Panel C is a 2-dimensional “slice” of the colon from a CT scan, revealing a polyp on a stalk (white arrow). Panel D is a photograph of the same polyp taken during conventional colonoscopy. Copyright New England Journal of Medicine 2003

The Black Arrow in Panel B and D indicates the appendix opening.

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